A systematic review and meta-analysis of the association between uric acid levels and chronic kidney disease

Association of uric acid with body adiposity and biochemical parameters in kidney transplant patients

BACKGROUND

Obesity and various biochemical parameters, including triglycerides, cholesterol, glucose, C-reactive protein, and estimated glomerular filtration rate, have been linked to elevated uric acid (UA) levels in populations with normal kidney function due to decreased UA excretion and/or increased UA synthesis. However, it remains unclear whether all these factors exhibit similar associations with UA levels in clinical populations characterized by compromised renal function, such as kidney transplant patients (KTPs).

OBJECTIVE

To evaluate whether serum UA levels are associated with body adiposity and biochemical parameters in KTPs.

METHODS

A cross-sectional study involving 113 KTPs was conducted. Body fat was estimated using bioelectrical impedance, and waist circumference was measured using an inelastic tape. Serum levels of UA, creatinine, glucose, triglycerides, total cholesterol, and its fractions were measured using the colorimetric method. C-reactive protein levels were assessed using the immunoturbidimetric method, and urea levels were determined via enzymatic kinetics. Glomerular filtration rate was estimated using the chronic kidney disease epidemiology collaboration equation. Linear regression analyses were employed to assess the association between serum UA levels and body adiposity as well as biochemical parameters, while adjusting for confounders.

RESULTS

Serum UA levels exhibited a positive association with creatinine (β = 0.402; p = 0.013) and urea (β = 0.024; p = 0.001), while demonstrating an inverse association with estimated glomerular filtration rate (β = -0.030; p < 0.001). However, serum UA levels were not significantly associated with fat mass (both in kilograms and as a percentage), waist circumference, triglycerides, C-reactive protein, glucose, HDL cholesterol, LDL cholesterol, VLDL cholesterol, or total cholesterol.

CONCLUSION

Serum UA levels are only associated with biochemical parameters linked to renal function in KTPs. Consequently, in individuals with suboptimal renal function, such as KTPs, UA does not exhibit associations with other biochemical parameters and body adiposity, as commonly observed in non-renal disease populations.

Effects of allopurinol and febuxostat on uric acid transport and transporter expression in human umbilical vein endothelial cells

Uric acid induces radical oxygen species formation, endothelial inflammation, and endothelial dysfunction which contributes to the progression of atherosclerosis. Febuxostat inhibits BCRP- and allopurinol stimulates MRP4-mediated uric acid efflux in human embryonic kidney cells. We hypothesized that endothelial cells express uric acid transporters that regulate intracellular uric acid concentration and that modulation of these transporters by febuxostat and allopurinol contributes to their different impact on cardiovascular mortality. The aim of this study was to explore a potential difference between the effect of febuxostat and allopurinol on uric acid uptake by human umbilical vein endothelial cells. Febuxostat increased intracellular uric acid concentrations compared with control. In contrast, allopurinol did not affect intracellular uric acid concentration. In line with this observation, febuxostat increased mRNA expression of GLUT9 and reduced MRP4 expression, while allopurinol did not affect mRNA expression of these uric acid transporters. These findings provide a possible pathophysiological pathway which could explain the higher cardiovascular mortality for febuxostat compared to allopurinol but should be explored further.

Uric acid-lowering effect of harpagoside and its protective effect against hyperuricemia-induced renal injury in mice

Hyperuricemia (HUA) is caused by increased synthesis and/or insufficient excretion of uric acid (UA). Long-lasting HUA may lead to a number of diseases including gout and kidney injury. Harpagoside (Harp) is a bioactive compound with potent anti-inflammatory activity from the roots of Scrophularia ningpoensis. Nevertheless, its potential effect on HUA was not reported. The anti-HUA and nephroprotective effects of Harp on HUA mice were assessed by biochemical and histological analysis. The proteins responsible for UA production and transportation were investigated to figure out its anti-HUA mechanism, while proteins related to NF-κB/NLRP3 pathway were evaluated to reveal its nephroprotective mechanism. The safety was evaluated by testing its effect on body weight and organ coefficients. The results showed that Harp significantly reduced the SUA level and protected the kidney against HUA-induced injury but had no negative effect on safety. Mechanistically, Harp significantly reduced UA production by acting as inhibitors of xanthine oxidase (XOD) and adenosine deaminase (ADA) and decreased UA excretion by acting as activators of ABCG2, OAT1 and inhibitors of GLUT9 and URAT1. Moreover, Harp markedly reduced infiltration of inflammatory cells and down-regulated expressions of TNF-α, NF-κB, NLRP3 and IL-1β in the kidney. Harp was a promising anti-HUA agent.

Assessment of the efficacy of alkaline water in conjunction with conventional medication for the treatment of chronic gouty arthritis: A randomized controlled study

BACKGROUND

Chronic gouty arthritis, a prevalent metabolic disorder, has prompted interest in the role of diet and lifestyle in its management. This study examines alkaline water as a non-pharmacological adjunct to traditional medicine, hypothesizing its positive effects on uric acid levels and gout symptoms.

METHODS

In this research, 400 chronic arthritis patients from Guangdong Hydropower Hospital (September 2021-September 2023) were randomly assigned to groups receiving varying concentrations of alkaline water alongside conventional Western medicine, or Western medicine alone. A 1-year follow-up involved assessments using visual analogue scales, joint swelling scores, functional assessment scales, and biochemical markers (serum uric acid, creatinine, urea nitrogen) for comprehensive evaluation.

RESULTS

Pain relief: High-concentration alkaline water significantly reduced VAS pain scores posttreatment (P < .05). Joint swelling: Greatest improvement observed in high-concentration group (P < .001). Daily activity capability: Notable enhancements in daily activity scores in experimental groups (P < .05). Range of joint motion: All groups showed significant improvement posttreatment (P < .05). Inflammatory markers: Experimental groups experienced a notable decrease in C-reactive protein, especially in the low concentration group (P < .001). Erythrocyte sedimentation rate decreases were marginal and not statistically significant (P > .05). Interleukin-1β and tumor necrosis factor-α levels significantly decreased, particularly in the low concentration group. Serum uric acid levels: Significant reduction in serum uric acid observed in all alkaline water groups (P < .05), contrasting with the control group.

CONCLUSION

Alkaline water, particularly at high concentrations, effectively alleviated pain, reduced joint swelling, enhanced daily activities, and improved joint motion in chronic gouty arthritis treatment. It significantly reduced key inflammatory markers (C-reactive protein, interleukin-1β, tumor necrosis factor-α) and serum uric acid levels, suggesting its potential as a valuable adjunct in gout management. The limited impact on erythrocyte sedimentation rate warrants further investigation.

Effect of uric acid reduction on chronic kidney disease. Systematic review and meta-analysis

Accumulating evidence suggests that hyperuricemia is a pathological factor in the development and progression of chronic kidney disease. However, the potential benefit afforded by the control of uric acid (UA) is controversial. Individual studies show discrepant results, and most existing meta-analysis, especially those including the larger number of studies, lack a placebo or control group as they aim to compare efficacy between drugs. On these grounds, we performed a me-ta-analysis restricted to studies including the action of any anti-gout therapies referenced to a control or placebo arm. This approach allows for a clearer association between UA reduction and renal effect. Of the twenty-nine papers included, most used allopurinol and febuxostat and, therefore, solid conclusions could only be obtained for these drugs. Both were very effective in reducing UA, but only allopurinol was able to significantly improve glomerular filtration rate (GFR), although not in a dose-dependent manner. These results raised doubts as to whether it is the hypouricemic effect of anti-gout drugs, or a pleiotropic effect, what provides protection of kidney function. Accordingly, in a correlation study that we next performed between UA reduction and GFR improvement, no association was found, which suggests that additional mechanisms may be involved. Of note, most trials show large inter-individual response variability, probably because they included patients with heterogeneous phenotypes and pathological characteristics, including different stages of CKD and comorbidities. This highlights the need to sub classify the effect of UA-lowering therapies according to the pathological scenario, in order to identify those CKD patients that may benefit most from them. Systematic Review Registration: CRD42022306646 https://www.crd.york.ac.uk/prospero/.

Prevalence and Risk Factors of Hyperuricemia Among Young and Middle-Aged Tibetan Men Living at Ultrahigh Altitudes: A Cross-Sectional Study

He, Ben, Jiayue Feng, Yan Shu, Lichun Yang, Zepin He, Kanxiu Liao, Hui Zhuo, and Hui Li. Prevalence and risk factors of hyperuricemia among young and middle-aged Tibetan men living at ultrahigh altitudes: a cross-sectional study. High Alt Med Biol. 25:42-48, 2024. Background: Few studies have examined the prevalence or risk factors of hyperuricemia among populations living at ultrahigh altitudes. Here we examined the prevalence of hyperuricemia and factors associated with it among young and middle-aged Tibetan men living at ultrahigh altitudes. Methods: This cross-sectional study analyzed 672 Tibetan men 18-60 years old living on the Qinghai-Tibet Plateau (mean altitude 4,014 m) within the county of Litang in the Ganzi Tibetan autonomous prefecture of Sichuan Province, China. Demographic and clinical data were collected from self-administered questionnaires, physical examinations and laboratory tests. Participants whose blood uric acid (UA) contained >420 μmol/l were classified as having hyperuricemia. Results: Of the 672 men analyzed, 332 (49.4%) had hyperuricemia. Multivariate logistic regression showed risk of hyperuricemia to correlate positively with body mass index (per 1 U increase: odds ratio [OR] 1.172, 95% confidence interval [CI] 1.1066-1.243), triglycerides (OR 1.408, 95% CI 1.084-1.828), red blood cell count (OR 1.376, 95% CI 1.009-1.875), and creatinine level (per 1 U increase: OR 1.051, 95% CI 1.033-1.070). Conversely, risk of hyperuricemia correlated negatively with the presence of diabetes mellitus (OR 0.412, 95% CI 0.175-0.968). Subgroup analyses showed that prevalence of hyperuricemia was significantly higher among those with polycythemia than among those without it, and that UA levels correlated positively with hematocrit and hemoglobin levels. Conclusions: Hyperuricemia is an important public health problem among Tibetan men living at ultrahigh altitudes in Ganzi autonomous prefecture. The region urgently requires appropriate prevention and management efforts.

Fuling-Zexie formula attenuates hyperuricemia-induced nephropathy and inhibits JAK2/STAT3 signaling and NLRP3 inflammasome activation in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Fuling-Zexie (FZ) formula, a traditional Chinese herbal prescription composed of Poria cocos (Schwan.) Wolf. (Poria), Pueraria lobate (Willd.) Howe. (Puerariae Lobatae Radix), Alisma orientale (Sam.) Julep. (Alismatis Rhizoma), and Atractylodes lancea (Thunb.) Dc. (Atractylodis Rhizoma), has been clinically used to ameliorate hyperuricemia (HUA) and its associated renal injury.

AIM OF STUDY

This study aims to explore the action and mechanism of FZ on renal inflammation and dysfunction caused by HUA.

MATERIALS AND METHODS

FZ was orally administered to rapid HUA mouse induced by potassium oxonate (PO) and hypoxanthine (HX) for 7 days. Serum levels of uric acid (UA), creatinine (CRE), blood urea nitrogen (BUN), xanthine oxidase (XOD), adenosine deaminase (ADA), alanine aminotransferase (ALT), aspartate aminotransferase (AST), urine levels of UA, CRE and urinary albumin were determined by biochemical assays. Serum levels of interleukin (IL)-1β and IL-6 were tested by ELISA. Hematoxylin-eosin and Masson staining were used to examine kidney and liver histopathological alterations. The expressions of renal glucose transporter 9 (GLUT9), ATP-binding cassette subfamily G member 2 (ABCG2), organic anion transporter 1 (OAT1), phospho-janus kinase 2 (p-JAK2), p-signal transducer and activator of transcription 3 (p-STAT3), suppression of cytokine signaling 3 (SOCS3), NLR family pyrin domain containing 3 (NLRP3), apoptosis-associated speck-like protein (ASC), and cleaved-cysteinyl aspartate specific proteinase-1 (cleaved-Cas-1) were detected by western blots. The potential protein targets and pathways of FZ intervention on HUA were predicted by network pharmacology. The constituents in FZ aqueous extract were analyzed by UPLC-MS.

RESULTS

FZ reduced serum UA, CRE, BUN, and urinary albumin and increased urine UA, CRE levels in HUA mice. In addition, the treatment with FZ to HUA mice inhibited the elevated serum levels of XOD and ADA, and regulated renal urate transports including OAT1, GLUT9 and ABCG2. FZ also attenuated kidney inflammation and fibrosis and downregulated the expressions of IL-1β, p-JAK2, p-STAT3, SOCS3, IL-6, NLRP3, ASC, and cleaved-Cas-1. Thirteen compounds were identified in the FG, including L-phenylalanine, D-tryptophan, 3'-hydroxypuerarin, Puerarin, 3'-Methoxy Puerarin, Daidzin, Pueroside A, formononetin-8-C- [xylosyl (1→6)]-glucoside, Ononin, Alisol I 23-acetate, 16-oxo-alisol A, Alisol C and Alisol A.

CONCLUSION

FZ inhibits serum UA generation and promotes urine UA excretion as well as attenuates kidney inflammation and fibrosis in HUA mouse with nephropathy. The underlying mechanism of its action may be associated with suppression of the JAK2/STAT3 signaling pathway and NLRP3 inflammasome activation. This formula may offer a novel source for developing anti-HUA drugs.

Efficacy of comprehensive group-based education in lowering body weight, uric acid levels, and diuretic use in patients with chronic kidney disease: a retrospective study

BACKGROUND

Patient education for the management of chronic kidney disease (CKD) is attracting attention. Therefore, this study aimed to analyze changes in body weight, uric acid, and estimated-glomerular filtration rate (eGFR) in patients with CKD after a group-based education during admission.

METHODS

Overall, 157 patients with CKD, who were discharged from the nephrology department of our hospital between January 2015 and October 2019, received group-based education or individual-based education by nurses at admission. Deltas of body weight, uric acid, and eGFR, 6 months from baseline, were compared between group- and individual-based education using the Wilcoxon rank sum test.

RESULTS

In total, 60 patients receiving group-based education (G group, n =35) or individual-based education (I group, n =25) during admission were included in this retrospective study. The patient characteristics at baseline were as follows: age mean, 72 ± SD 9; 16 females and 44 males; body weight, 62 ± 17 kg; eGFR median, 21 (IQR: 14, 29) mL/min/1.73 m2; UA, 7 (6.1, 7.5) mg/dL; and estimated intake of salt 6.9 (6.2, 8.4) g/day. Delta eGFR (mL/min/1.73 m2) was -1 (-3, 3) for G group and -1 (-2.5, 2) for I group (p = 0.8039). Delta body weight (kg) was -0.4 (-1.6, 0) for G group and 0 (-0.45, 0.95) for I group (p = 0.0597). Delta uric acid (mg/dL) was -1.1 (-1.6, 0.1) for G group and -0.2 (-1.1, 0.5) for I group (p = 0.0567). In patients with higher sodium intake (≥ 117.4 mEq/day), delta body weight was significantly lower in the group-based education group than in the individual-based education group (p = 0.0398).

CONCLUSIONS

A comprehensive group-based education in patients with CKD may effectively suppress body weight and uric acid in 6 months along with less frequent diuretic use.

Relationship between serum uric acid and estimated glomerular filtration rate in adolescents aged 12-19 years with different body mass indices: a cross-sectional study

Background

Globally, chronic kidney disease (CKD) is a growing public health concern. Serum uric acid (SUA) is an easily detectable and readily available biochemical indicator that has long been recognized as an independent risk factor for CKD. In addition, studies have indicated a potential relationship between SUA and body mass index (BMI). However, studies on the effect of SUA levels on the estimated glomerular filtration rate (eGFR) in adolescents with different BMIs are very rare.

Methods

Weighted multiple regression analysis was used to estimate the independent relationship between SUA and log-transformed eGFR. Additionally, we used a weighted generalized additive model and smooth curve fitting to describe the nonlinear relationships in the subgroup analysis.

Results

First, SUA was negatively associated with log-transformed eGFR even after adjusting for all covariates (β=-0.0177, 95% CI: -0.0203-0.0151, P<0.0001). Second, the results of the stratified analysis found that after adjusting for all covariates, the decrease in log-transformed eGFR due to changes in per SUA levels (Per 1, mg/dL increase) was elevated in female adolescents (β=-0.0177, 95% CI: -0.0216, -0.0138, P<0.0001), adolescents aged 12-15 years (β=-0.0163, 95% CI: -0.0200, -0.0125, P<0.0001) and black (β=-0.0199, 95% CI: -0.0251, -0.0148, P<0.0001) adolescents. Furthermore, we found that adolescents with a higher BMI had higher SUA levels, and the effect of SUA on eGFR was significantly higher in underweight adolescents (β=-0.0386, 95% CI: (-0.0550, -0.0223), P<0.0001).

Conclusion

SUA was negatively associated with the eGFR in adolescents aged 12-19 years. Furthermore, we found for the first time that SUA affects the eGFR differently in adolescents with different BMIs. This effect was particularly significant in underweight adolescents.

Serum Urate and Risk of Chronic Kidney Disease: A Mendelian Randomization Study Using Taiwan Biobank

OBJECTIVE

To evaluate the association between serum urate and risk of incident chronic kidney disease (CKD) and to assess whether serum urate plays a causal role in CKD.

PATIENTS AND METHODS

We conducted a prospective cohort study and Mendelian randomization analysis that analyzed longitudinal data from the Taiwan Biobank between January 1, 2012, and December 31, 2021.

RESULTS

A total of 34,831 individuals met the inclusion criteria, of which 4697 (13.5%) had hyperuricemia. After a median (interquartile range) follow-up of 4.1 (3.1-4.9) years, 429 participants developed CKD. After adjustment for age, sex, and comorbid conditions, each mg/dL increase in serum urate was associated with a 15% higher risk of incident CKD (HR, 1.15; 95% CI, 1.08 to 1.24; P<.001). The genetic risk score and seven Mendelian randomization methods revealed no significant association between serum urate levels and the risk of incident CKD (HR, 1.03; 95% CI, 0.72 to 1.46; P=0.89; all P>.05 for 7 Mendelian randomization methods).

CONCLUSION

This prospective, population-based cohort study showed that elevated serum urate is a significant risk factor for incident CKD; however, Mendelian randomization analyses failed to provide evidence that serum urate had a causal effect on CKD in the East Asian population.

Association of hyperuricemia with cardiovascular diseases: current evidence

The aim of the present study is to present a historical and unified perspective on the association of serum uric acid (SUA) in the cause of cardiovascular diseases (CVDs). The association of hyperuricemia (HUC) with CVD begun to be appreciated in the middle 1950s and early 1990s when clinical evidence was shown on the association of HUC with CVD. However, this association was disputed by several investigators including the Framingham group and by professional societies, like the American Heart Association and the American Society of Hypertension. This dispute was weakened or reversed by later studies, which showed a positive association of HUC with CVD, CHD, HF, CKD, and stroke, mediated by several risk factors, both molecular such as, oxidative stress, inflammatory stress, insulin resistance, and endothelial dysfunction, as well as clinical factors such as, atherosclerosis, hypertension, metabolic syndrome, and type 2 diabetes mellitus. The great majority of recent studies show a positive association of HUC with CVDs, and CKD. However, the cutoff of the damaging levels of SUA have not been established as yet. The European Society of Hypertension (ESH) Treatment Guidelines have proposed a cutoff level of SUA for CVD > 7 mg/dl for men and > 6 mg/dl for women. In contrast, the URRAH study has shown a SUA level of 4.7 mg/dl for all-cause mortality and 5.6 mg/dl for CV mortality. These levels are lower than the SUA levels proposed by the ESH, which are consistent with HUC. For a better understanding of this association, a Medline search of the English literature was conducted between 2015 and 2022 and 44 pertinent papers were selected. These papers together with collateral literature will be discussed in this review.

Altered Serum Uric Acid Levels in Kidney Disorders

Serum uric acid levels are altered by kidney disorders because the kidneys play a dominant role in uric acid excretion. Here, major kidney disorders which accompany hyperuricemia or hypouricemia, including their pathophysiology, are discussed. Chronic kidney disease (CKD) and hyperuricemia are frequently associated, but recent clinical trials have not supported the pathogenic roles of hyperuricemia in CKD incidence and progression. Diabetes mellitus (DM) is often associated with hyperuricemia, and hyperuricemia may be associated with an increased risk of diabetic kidney disease in patients with type 2 DM. Sodium-glucose cotransporter 2 inhibitors have a uricosuric effect and can relieve hyperuricemia in DM. Autosomal dominant tubulointerstitial kidney disease (ADTKD) is an important hereditary kidney disease, mainly caused by mutations of uromodulin (UMOD) or mucin-1 (MUC-1). Hyperuricemia and gout are the major clinical manifestations of ADTKD-UMOD and ADTKD-MUC1. Renal hypouricemia is caused by URAT1 or GLUT9 loss-of-function mutations and renders patients susceptible to exercise-induced acute kidney injury, probably because of excessive urinary uric acid excretion. Hypouricemia derived from renal uric acid wasting is a component of Fanconi syndrome, which can be hereditary or acquired. During treatment for human immunodeficiency virus, hepatitis B or cytomegalovirus, tenofovir, adefovir, and cidofovir may cause drug-induced renal Fanconi syndrome. In coronavirus disease 2019, hypouricemia due to proximal tubular injury is related to disease severity, including respiratory failure. Finally, serum uric acid and the fractional excretion of uric acid are indicative of plasma volume status; hyperuricemia caused by the enhanced uric acid reabsorption can be induced by volume depletion, and hypouricemia caused by an increased fractional excretion of uric acid is the characteristic finding in syndromes of inappropriate anti-diuresis, cerebral/renal salt wasting, and thiazide-induced hyponatremia. Molecular mechanisms by which uric acid transport is dysregulated in volume or water balance disorders need to be investigated.

The paradoxical relation between serum uric acid and outcomes of hip fracture in older patients after surgery: A 1-year follow-up study

BACKGROUND

The relation between serum uric acid and bone metabolism has been reported in many studies, but few studies have focused on serum uric acid and fracture rehabilitation. We aimed to explore the potential relationships between serum uric acid and outcomes of hip fractures.

METHODS

A total of 742 patients with hip fractures who underwent surgeries between December 2017 and February 2021 and met the inclusion criteria were included. The data of male and female patients were analyzed separately. Cox models with different adjusted forms were performed to explore the potential risk factors, and restricted cubic splines were used to determine the nonlinear relationships between serum uric acid and outcomes and optimal cutoff points of serum uric acid. Then, the outcomes were analyzed in the groups divided by cutoff points mentioned above, as well as groups divided by the diagnosis of hyperuricemia or gout.

RESULTS

Cox analysis showed that hyperuricemia or gout was associated with increased death risk, and a typical J-shaped curve was observed in the restricted cubic spline. For male patients, a serum uric acid of high level may relate to a high risk of 6-month (P = .008) and 1-year (P = .016) mortality, and a serum uric acid of low level may predict a poor 6-month free walking ability. For female patients, both a serum uric acid of high level and low level were associated with poor 1-year survival (all P < .05), and a serum uric acid of high level may relate to poor 6-month (P = .001) and 1-year (P = .001) free walking ability.

CONCLUSION

Patients with hyperuricemia or gout or patients with high and low levels of serum uric acid may face poor outcomes of hip fractures.